This application relates generally to gas turbine engine rotor assemblies and, more particularly, to bearing assemblies for gas turbine engine rotor assemblies.
Gas turbine engines typically includes a fan rotor assembly, a compressor, and a turbine. The fan rotor assembly includes a fan including an array of fan blades extending radially outward from a rotor shaft. The rotor shaft transfers power and rotary motion from the turbine to the compressor and the fan, and is supported longitudinally with a plurality of bearing assemblies. Bearing assemblies support the rotor shaft and typically include rolling elements located within an inner race and an outer race.
Additionally, at least some known bearing assemblies include a plurality of identical springs attached to the bearing outer race. The springs are spaced equally in a single row that extends circumferentially around the rotor shaft to provide radial stiffness to the bearing and to center the outer race with respect to the support frame. A first end of the springs is attached to the bearing assembly outer race, and a second end of the springs is attached to a flange coupled to a support frame.
During operation, an unbalance within the engine may cause the engine rotor shaft to displace radially. The radial displacements of the shaft are transmitted to the bearing assembly and may cause the bearing outer race to orbit within the support frame. The rotation of the outer race may cause the springs to fail in bending. After spring failure, the outer race is not axially retained, and axial movement of the outer race may permit the rotor to inadvertently contact the support frame, and may cause unpredictable static radial loads to be transmitted to the fan rotor assembly, and dynamic radial loads to be transmitted to the support structure.
In one aspect of the invention, a bearing assembly for a gas turbine engine rotor is provided. The bearing assembly includes a damper bearing configured to support the rotor, a bearing centering sub-assembly configured to position the damper bearing relative to the rotor, and a retainer. The damper bearing includes a frame that defines a bearing bore, an inner race, and an outer race, said inner and outer races within said bearing bore. The bearing centering apparatus sub-assembly includes a plurality of first springs and a plurality of second springs. The retainer is coupled to the bearing housing and is configured to maintain an axial position of at least one of the bearing inner race and the bearing outer race.
In another aspect, a method for reducing dynamic loading of a gas turbine engine rotor assembly is provided. The engine includes a rotor shaft, a support frame, and a bearing assembly including a bearing centering sub-assembly and a damper bearing. The bearing centering sub-assembly includes a plurality of first springs and a plurality of second springs. The method includes supporting the rotor shaft on the support frame with the bearing assembly, coupling the bearing centering sub-assembly first spring to the bearing assembly second spring such that the each of the first springs is radially aligned with respect to each of the second springs, and operating the gas turbine engine such that radial forces within the rotor shaft are transmitted through the bearing centering sub-assembly to the support frame.
In a further aspect, a rotor assembly including a rotor shaft, a support frame, a bearing assembly, and a retainer is provided. The support frame defines a bearing bore. The bearing assembly is configured to support the rotor shaft on the support frame such that dynamic loads to the support frame are reduced. The bearing assembly includes a bearing centering sub-assembly, a damper bearing, and a retainer. The bearing centering sub-assembly is configured to position the bearing relative to the rotor shaft. The bearing centering sub-assembly includes a plurality of first springs and a plurality of second springs. Each of said first springs radially aligned with respect to each of the second springs. The damper bearing includes an inner race and an outer race. The inner and outer races are within the support frame bore. The retainer is coupled to the support frame and is configured to maintain an axial position of at least one of the bearing inner race and the bearing outer race relative to the support frame.